1. Field
Embodiments relate to a rotation angle detecting apparatus to detect a rotation angle of a rotating member, and more particularly relate to a rotation angle detecting apparatus that is susceptible to external shock, such as an accelerator pedal device, which controls the amount of intake air into an engine on the basis of a depression angle.
2. Description of the Related Art
A conventional rotation angle detecting apparatus for detecting a rotation angle of an accelerator pedal, for example, is mounted with a magnet to generate a magnetic field on the accelerator pedal side, and a sensor to detect a behavior of the magnetic field on the side where a housing, for example, is fixed. The magnet is press-fitted and fixed to a circumference with a rotation axis of the accelerator pedal as its center. The sensor converts the density of a magnetic flux, the angle of which changes as the magnet rotates when the accelerator pedal is stepped on, to an electrical signal and outputs this electrical signal. The amount of intake air into the engine is controlled by inputting this output electrical signal to a controller that controls the opening of a throttle valve that adjusts the amount of intake air into the engine. Incidentally, when the magnet is not completely fixed to the accelerator pedal, it is difficult for the sensor to accurately detect the depression angle of the accelerator pedal, which degrades the accuracy of controlling the amount of intake air.
There is known a resin accelerator pedal device that uses heat-softened resin to caulk-fix a magnet that is press-fitted to an accelerator pedal, thereby preventing the magnet from falling off the accelerator pedal such as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2008-201312.
There is also known a compact motor in which a magnet inserted into a frame is fixed to the frame by being pressed against the frame using a ring-shaped plate spring embedded in an inner peripheral wall of the frame such as disclosed in, for example, Japanese Unexamined Utility Model Application Publication No. H5-11753.
In the rotation angle detecting apparatus for an accelerator pedal device that is described in Japanese Unexamined Patent Application Publication No. 2008-201312, when caulk-fixing the magnet by using the softened resin, the heat added at this time contracts/deforms the resin around the magnet. As a result, a small gap is generated around the magnet, causing misalignment and loosening. Moreover, when adhering the softened resin to the magnet, strong pressure and high heat are transmitted to the magnet, resulting in the risk of deteriorating the holding force and durability of the magnet. In addition, great number of management tasks are required such as examining the cross section of the resin that is deformed by caulking, as well as checking the holding force of the magnet, and the temperature, pressure and the time of application thereof need to be adjusted according to the type of the resin.
In the rotation angle detecting apparatus for a compact motor that is described in Japanese Unexamined Utility Model Application Publication No. H5-11753, the plate spring for fixing the magnet is supported at the section where the plate spring is embedded in the frame serving as a chassis. For this reason, the magnet might be removed relatively easily by external shock, deterioration of the section where the plate spring is embedded, and contraction due to the changes in the temperature. Furthermore, because the spring needs to be compressed when being attached to the frame, the accuracy of attaching the spring becomes unstable, making it difficult to fix the magnet stably.